In order to achieve the optimized configuration of inverter capability, especially in order to achieve a single machine with a high power as the power generation system capacity increases, the parallel of inverters becomes a technical development trend. The parallel of inverters has the following advantages: (1) it is convenient to enlarge the capacity of a grid-connected inverter; (2) the system cost is reduced due to devices sharing; (3) it is easy to realize group control, thereby increasing the system efficiency; and (4) for the MW-level parallel inverter system, a double-wound transformer instead of a double-split transformer may be used at the alternating-current side, thereby reducing the investment cost for the system.
In view of the above advantages, a parallel inverter system is widely used in a power station, especially in a new energy power generation system such as a photovoltaic power generation system. The ideal operating state of the parallel inverter system is that all of the inverter apparatuses in the parallel inverter system operate normally, but some abnormalities may occur due to various reasons. Taking a parallel inverter system including two inverter apparatuses as an example, in practice, one inverter apparatus may operate normally and the other inverter apparatus may be shut down due to a failure or other reasons, which causes the instability of the parallel inverter system.
Hence, it is a technical problem to be solved urgently by those skilled in the art that how to control some inverter apparatuses in the parallel inverter system to respond effectively in a case that the inverter apparatuses is needed to be shut down, so as to ensure the stable operation of the parallel inverter system.